Oil insulated transformer

Hi Gents. I've to use a transformer ( "R" Core), primary to mains and secondary (2 X 9 V) connected to high voltage source of about 8 kV. I am going, in order to improve primary to secondary insulation, to place this transformer in a paraffin oil "bath". Is it a good idea ?

Look for transformers with high isolation voltage to start. I found 2 to 3KV isolation transformers before in cheap price. Then dip in oil.

Yes, if you get under rated transformers, you need to dip in oil. This will hopefully eliminate the creepage path ( arc along surface). It is important to have transformers that have primary and secondary side by side with separate bobbins or at least has a divider. If the secondary is right on top of the primary, no oil is going to do much as they are in close contact, oil is not going to help much.